<!DOCTYPE html>
<html lang="">
    <head>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <meta name="robots" content="noodp" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge, chrome=1">
        <title>02 Mybatis Log 源码分析 - 暗夜零星</title><meta name="Description" content="mybatis log 的实现源码、原理解析。"><meta property="og:title" content="02 Mybatis Log 源码分析" />
<meta property="og:description" content="mybatis log 的实现源码、原理解析。" />
<meta property="og:type" content="article" />
<meta property="og:url" content="https://wlizhi.cc/posts/mybatis/02-mybatis-log/" /><meta property="og:image" content="https://wlizhi.cc/logo.png"/><meta property="article:section" content="posts" />
<meta property="article:published_time" content="2020-12-20T10:02:59+08:00" />
<meta property="article:modified_time" content="2020-12-20T10:02:59+08:00" />

<meta name="twitter:card" content="summary_large_image"/>
<meta name="twitter:image" content="https://wlizhi.cc/logo.png"/>

<meta name="twitter:title" content="02 Mybatis Log 源码分析"/>
<meta name="twitter:description" content="mybatis log 的实现源码、原理解析。"/>
<meta name="application-name" content="暗夜零星">
<meta name="apple-mobile-web-app-title" content="暗夜零星"><link rel="shortcut icon" type="image/x-icon" href="/favicon.ico" />
        <link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png">
        <link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png"><link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png"><link rel="manifest" href="/site.webmanifest"><link rel="canonical" href="https://wlizhi.cc/posts/mybatis/02-mybatis-log/" /><link rel="prev" href="https://wlizhi.cc/posts/mybatis/01-mybatis-structure/" /><link rel="next" href="https://wlizhi.cc/posts/mybatis/03-mybatis-pooled-data-source/" /><link rel="stylesheet" href="/lib/normalize/normalize.min.css"><link rel="stylesheet" href="/css/style.min.css"><link rel="stylesheet" href="/lib/fontawesome-free/all.min.css"><link rel="stylesheet" href="/lib/animate/animate.min.css"><script type="application/ld+json">
    {
        "@context": "http://schema.org",
        "@type": "BlogPosting",
        "headline": "02 Mybatis Log 源码分析",
        "inLanguage": "",
        "mainEntityOfPage": {
            "@type": "WebPage",
            "@id": "https:\/\/wlizhi.cc\/posts\/mybatis\/02-mybatis-log\/"
        },"genre": "posts","keywords": "mybatis源码","wordcount":  4192 ,
        "url": "https:\/\/wlizhi.cc\/posts\/mybatis\/02-mybatis-log\/","datePublished": "2020-12-20T10:02:59+08:00","dateModified": "2020-12-20T10:02:59+08:00","publisher": {
            "@type": "Organization",
            "name": "Wlizhi"},"author": {
                "@type": "Person",
                "name": "Wlizhi"
            },"description": "mybatis log 的实现源码、原理解析。"
    }
    </script></head>
    <body header-desktop="fixed" header-mobile="auto"><script type="text/javascript">(window.localStorage && localStorage.getItem('theme') ? localStorage.getItem('theme') === 'dark' : ('auto' === 'auto' ? window.matchMedia('(prefers-color-scheme: dark)').matches : 'auto' === 'dark')) && document.body.setAttribute('theme', 'dark');</script>

        <div id="mask"></div><div class="wrapper"><header class="desktop" id="header-desktop">
    <div class="header-wrapper">
        <div class="header-title">
            <a href="/" title="暗夜零星"><span class="header-title-pre"><i class='far fa-moon fa-fw'></i></span>暗夜零星</a>
        </div>
        <div class="menu">
            <div class="menu-inner"><a class="menu-item" href="/posts/"> 所有文章 </a><a class="menu-item" href="/tags/"> 标签 </a><a class="menu-item" href="/categories/"> 分类 </a><a class="menu-item" href="/message-board/"> 留言 </a><a class="menu-item" href="/about/"> 关于 </a><a class="menu-item" href="https://github.com/wlizhi" title="GitHub" rel="noopener noreffer" target="_blank"><i class='fab fa-github fa-fw'></i>  </a><a class="menu-item" href="https://gitee.com/wlizhi" title="Gitee" rel="noopener noreffer" target="_blank"><i class='fab fa-git fa-fw'></i>  </a><span class="menu-item delimiter"></span><span class="menu-item search" id="search-desktop">
                        <input type="text" placeholder="点击搜索..." id="search-input-desktop">
                        <a href="javascript:void(0);" class="search-button search-toggle" id="search-toggle-desktop" title="搜索">
                            <i class="fas fa-search fa-fw"></i>
                        </a>
                        <a href="javascript:void(0);" class="search-button search-clear" id="search-clear-desktop" title="清空">
                            <i class="fas fa-times-circle fa-fw"></i>
                        </a>
                        <span class="search-button search-loading" id="search-loading-desktop">
                            <i class="fas fa-spinner fa-fw fa-spin"></i>
                        </span>
                    </span><a href="javascript:void(0);" class="menu-item theme-switch" title="切换主题">
                    <i class="fas fa-adjust fa-fw"></i>
                </a>
            </div>
        </div>
    </div>
</header><header class="mobile" id="header-mobile">
    <div class="header-container">
        <div class="header-wrapper">
            <div class="header-title">
                <a href="/" title="暗夜零星"><span class="header-title-pre"><i class='far fa-moon fa-fw'></i></span>暗夜零星</a>
            </div>
            <div class="menu-toggle" id="menu-toggle-mobile">
                <span></span><span></span><span></span>
            </div>
        </div>
        <div class="menu" id="menu-mobile"><div class="search-wrapper">
                    <div class="search mobile" id="search-mobile">
                        <input type="text" placeholder="点击搜索..." id="search-input-mobile">
                        <a href="javascript:void(0);" class="search-button search-toggle" id="search-toggle-mobile" title="搜索">
                            <i class="fas fa-search fa-fw"></i>
                        </a>
                        <a href="javascript:void(0);" class="search-button search-clear" id="search-clear-mobile" title="清空">
                            <i class="fas fa-times-circle fa-fw"></i>
                        </a>
                        <span class="search-button search-loading" id="search-loading-mobile">
                            <i class="fas fa-spinner fa-fw fa-spin"></i>
                        </span>
                    </div>
                    <a href="javascript:void(0);" class="search-cancel" id="search-cancel-mobile">
                        取消
                    </a>
                </div><a class="menu-item" href="/posts/" title="">所有文章</a><a class="menu-item" href="/tags/" title="">标签</a><a class="menu-item" href="/categories/" title="">分类</a><a class="menu-item" href="/message-board/" title="">留言</a><a class="menu-item" href="/about/" title="">关于</a><a class="menu-item" href="https://github.com/wlizhi" title="GitHub" rel="noopener noreffer" target="_blank"><i class='fab fa-github fa-fw'></i></a><a class="menu-item" href="https://gitee.com/wlizhi" title="Gitee" rel="noopener noreffer" target="_blank"><i class='fab fa-git fa-fw'></i></a><a href="javascript:void(0);" class="menu-item theme-switch" title="切换主题">
                <i class="fas fa-adjust fa-fw"></i>
            </a></div>
    </div>
</header>
<div class="search-dropdown desktop">
    <div id="search-dropdown-desktop"></div>
</div>
<div class="search-dropdown mobile">
    <div id="search-dropdown-mobile"></div>
</div>
<main class="main">
                <div class="container"><div class="toc" id="toc-auto">
            <h2 class="toc-title">目录</h2>
            <div class="toc-content" id="toc-content-auto"></div>
        </div><article class="page single"><h1 class="single-title animated flipInX">02 Mybatis Log 源码分析</h1><div class="post-meta">
            <div class="post-meta-line"><span class="post-author"><a href="https://wlizhi.cc" title="Author" target="_blank" rel="noopener noreffer author" class="author"><i class="fas fa-user-circle fa-fw"></i>Wlizhi</a></span>&nbsp;<span class="post-category">收录于 <a href="/categories/mybatis/"><i class="far fa-folder fa-fw"></i>mybatis</a></span></div>
            <div class="post-meta-line"><i class="far fa-calendar-alt fa-fw"></i>&nbsp;<time datetime="2020-12-20">2020-12-20</time>&nbsp;<i class="fas fa-pencil-alt fa-fw"></i>&nbsp;约 4192 字&nbsp;
                <i class="far fa-clock fa-fw"></i>&nbsp;预计阅读 9 分钟&nbsp;<span id="/posts/mybatis/02-mybatis-log/" class="leancloud_visitors" data-flag-title="02 Mybatis Log 源码分析">
                        <i class="far fa-eye fa-fw"></i>&nbsp;<span class=leancloud-visitors-count></span>&nbsp;次阅读
                    </span>&nbsp;</div>
        </div><div class="details toc" id="toc-static"  kept="">
                <div class="details-summary toc-title">
                    <span>目录</span>
                    <span><i class="details-icon fas fa-angle-right"></i></span>
                </div>
                <div class="details-content toc-content" id="toc-content-static"><nav id="TableOfContents">
  <ul>
    <li><a href="#1-适配器模式">1 适配器模式</a></li>
    <li><a href="#2-代理模式">2 代理模式</a></li>
    <li><a href="#3-mybatis-log-模块核心类结构图">3 mybatis log 模块核心类结构图</a></li>
    <li><a href="#4-mybatis-log-模块的核心类">4 mybatis log 模块的核心类</a></li>
    <li><a href="#5-log工厂类-logfactory">5 Log工厂类 LogFactory</a></li>
    <li><a href="#6-mybatis-log-规范-log">6 mybatis Log 规范 Log</a></li>
    <li><a href="#7-日志增强基-basejdbclogger">7 日志增强基 BaseJdbcLogger</a></li>
    <li><a href="#8-连接日志增强-connectionlogger">8 连接日志增强 ConnectionLogger</a></li>
    <li><a href="#9-preparedstatementlogger">9 PreparedStatementLogger</a></li>
    <li><a href="#10-结果集日志增强-resultsetlogger">10 结果集日志增强 ResultSetLogger</a></li>
    <li><a href="#11-小结">11 小结</a></li>
  </ul>
</nav></div>
            </div><div class="content" id="content"><p>mybatis源码系列文章，示例中带有中文注释的源码 copy 自 <a href="https://gitee.com/wlizhi/mybatis-3" target="_blank" rel="noopener noreffer">https://gitee.com/wlizhi/mybatis-3</a></p>
<p>链接中源码是作者从 github 下载，并以自身理解对核心流程及主要节点做了详细的中文注释。</p>
<hr>
<h2 id="1-适配器模式">1 适配器模式</h2>
<p>适配器模式（Adapter Patter）是作为两个不兼容接口之间的桥梁，将一个类的接口转换成客户希望的另外一个接口。适配器模式使得原本由于接口不
兼容而不能一起工作的那些类可以一起工作。</p>
<p>适用场景：当调用双方都不太容易修改的时候，为了复用现有组件可以使用适配器模式；在系统中接入第三方组件的时候经常被使用到。</p>
<p>注意：如果系统中存在过多的适配器，会增加系统的复杂性，设计人员应考虑对其进行重构。</p>
<h2 id="2-代理模式">2 代理模式</h2>
<p>定义：给目标对象提供一个代理对象，并由代理对象控制对目标对象的引用。</p>
<p>目的：</p>
<ol>
<li>通过引入代理对象的方式来间接访问目标对象，防止直接访问目标对象给系统带来不必要的复杂性。</li>
<li>通过代理对象对原有的业务增强。</li>
</ol>
<h2 id="3-mybatis-log-模块核心类结构图">3 mybatis log 模块核心类结构图</h2>
<p><img
        class="lazyload"
        src="/svg/loading.min.svg"
        data-src="https://oss.wlizhi.cc/blog/mybatis/mybatis-log-class-structure.png"
        data-srcset="https://oss.wlizhi.cc/blog/mybatis/mybatis-log-class-structure.png, https://oss.wlizhi.cc/blog/mybatis/mybatis-log-class-structure.png 1.5x, https://oss.wlizhi.cc/blog/mybatis/mybatis-log-class-structure.png 2x"
        data-sizes="auto"
        alt="https://oss.wlizhi.cc/blog/mybatis/mybatis-log-class-structure.png"
        title="mybatis-log-class-structure.png" /></p>
<h2 id="4-mybatis-log-模块的核心类">4 mybatis log 模块的核心类</h2>
<ul>
<li>LogFactory log对象工厂</li>
<li>Log mybatis 中自定义的一个 log 接口。使用了适配器模式，所有的第三方日志组件引入后，通过适配类，最终都会被转换为 Log 类型，mybatis 源码中的日志，统一使用 Log 接口。</li>
<li>BaseJdbcLogger jdbc包中所有日志增强的抽象基类，使用动态代理对目标进行日志增强。
<ul>
<li>ConnectionLogger 对 Connection 的日志增强类。</li>
<li>PreparedStatementLogger 对 PreparedStatement 的日志增强类。</li>
<li>ResultSetLogger 对 ResultSet 的日志增强类。</li>
<li>StatementLogger 对 Statement 的日志增强类。（一般使用 PreparedStatementLogger，且与前者原理相同，不列举。）</li>
</ul>
</li>
</ul>
<h2 id="5-log工厂类-logfactory">5 Log工厂类 LogFactory</h2>
<p>在类加载器加载 LogFactory 时，通过静态代码块，按照一定顺序，加载第三方日志组件，只要有一个加载成功，下面的就不再加载。</p>
<p>第三方日志组件加载优先级：<code>slf4j -&gt; commonsLogging -&gt; log4J2 -&gt; log4j -&gt; JdkLog</code></p>
<p>加载后将对应的日志组件的构造函数缓存到静态成员中。最终通过 <code>LogFactory.getLog(Class&lt;?&gt; clazz)</code> 进行日志对象的获取。</p>
<p>源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span><span class="lnt">19
</span><span class="lnt">20
</span><span class="lnt">21
</span><span class="lnt">22
</span><span class="lnt">23
</span><span class="lnt">24
</span><span class="lnt">25
</span><span class="lnt">26
</span><span class="lnt">27
</span><span class="lnt">28
</span><span class="lnt">29
</span><span class="lnt">30
</span><span class="lnt">31
</span><span class="lnt">32
</span><span class="lnt">33
</span><span class="lnt">34
</span><span class="lnt">35
</span><span class="lnt">36
</span><span class="lnt">37
</span><span class="lnt">38
</span><span class="lnt">39
</span><span class="lnt">40
</span><span class="lnt">41
</span><span class="lnt">42
</span><span class="lnt">43
</span><span class="lnt">44
</span><span class="lnt">45
</span><span class="lnt">46
</span><span class="lnt">47
</span><span class="lnt">48
</span><span class="lnt">49
</span><span class="lnt">50
</span><span class="lnt">51
</span><span class="lnt">52
</span><span class="lnt">53
</span><span class="lnt">54
</span><span class="lnt">55
</span><span class="lnt">56
</span><span class="lnt">57
</span><span class="lnt">58
</span><span class="lnt">59
</span><span class="lnt">60
</span><span class="lnt">61
</span><span class="lnt">62
</span><span class="lnt">63
</span><span class="lnt">64
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">LogFactory</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">  <span class="cm">/**
</span></span></span><span class="line"><span class="cl"><span class="cm">   * Marker to be used by logging implementations that support markers.
</span></span></span><span class="line"><span class="cl"><span class="cm">   */</span>
</span></span><span class="line"><span class="cl">  <span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">MARKER</span> <span class="o">=</span> <span class="s">&#34;MYBATIS&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">  <span class="c1">// 选择的第三方日志组件适配器的构造方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>  <span class="kd">private</span> <span class="kd">static</span> <span class="n">Constructor</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Log</span><span class="o">&gt;</span> <span class="n">logConstructor</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">  <span class="kd">static</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="c1">// 注意这里实在静态代码块中执行，在类加载器，第一次加载 LogFactory 时，就会执行这块代码，进行日志具体实现的初始化。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="c1">// 按照优先级尝试加载日志实现类。第三方日志插件加载优先级： slf4j -&gt; commonsLogging -&gt; log4J2 -&gt; log4j -&gt; JdkLog
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useSlf4jLogging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useCommonsLogging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useLog4J2Logging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useLog4JLogging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useJdkLogging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="n">tryImplementation</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">::</span><span class="n">useNoLogging</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">  <span class="o">}</span>
</span></span><span class="line"><span class="cl">  
</span></span><span class="line"><span class="cl">  <span class="cm">/** 构造函数私有，不允许外界创建该类实例 */</span>
</span></span><span class="line"><span class="cl">  <span class="kd">private</span> <span class="nf">LogFactory</span><span class="o">()</span> <span class="o">{</span> <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">  <span class="kd">public</span> <span class="kd">static</span> <span class="n">Log</span> <span class="nf">getLog</span><span class="o">(</span><span class="n">Class</span><span class="o">&lt;?&gt;</span> <span class="n">clazz</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="k">return</span> <span class="n">getLog</span><span class="o">(</span><span class="n">clazz</span><span class="o">.</span><span class="na">getName</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">  <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">  <span class="kd">public</span> <span class="kd">static</span> <span class="n">Log</span> <span class="nf">getLog</span><span class="o">(</span><span class="n">String</span> <span class="n">logger</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="k">try</span> <span class="o">{</span><span class="c1">// 获取log对象，通过静态块中加载log实现类时，缓存的log实现构造函数，以反射的方式创建log对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>      <span class="k">return</span> <span class="n">logConstructor</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">logger</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">      <span class="k">throw</span> <span class="k">new</span> <span class="n">LogException</span><span class="o">(</span><span class="s">&#34;Error creating logger for logger &#34;</span> <span class="o">+</span> <span class="n">logger</span> <span class="o">+</span> <span class="s">&#34;.  Cause: &#34;</span> <span class="o">+</span> <span class="n">t</span><span class="o">,</span> <span class="n">t</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl">  <span class="o">}</span>
</span></span><span class="line"><span class="cl">  <span class="c1">// 省略部分方法...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>
</span></span><span class="line"><span class="cl">  <span class="kd">private</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">tryImplementation</span><span class="o">(</span><span class="n">Runnable</span> <span class="n">runnable</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="c1">// 这个方法是加载log的方法。当构造方法为空，才执行方法。如果加载不到，则会忽略异常。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="k">if</span> <span class="o">(</span><span class="n">logConstructor</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">      <span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="n">runnable</span><span class="o">.</span><span class="na">run</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">      <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 注意这里忽略了异常，即当加载一个log实现，加载不到时，就会尝试加载另一种实现。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="c1">// 而加载不到的实现会抛出 java.lang.NoClassDefFoundError 到这里，最终会忽略掉异常。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="c1">// ignore
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>      <span class="o">}</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl">  <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">  <span class="c1">// 通过指定的 log 类来初始化构造方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>  <span class="kd">private</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">setImplementation</span><span class="o">(</span><span class="n">Class</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Log</span><span class="o">&gt;</span> <span class="n">implClass</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">      <span class="c1">// 反射创建 log 实例。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>      <span class="n">Constructor</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Log</span><span class="o">&gt;</span> <span class="n">candidate</span> <span class="o">=</span> <span class="n">implClass</span><span class="o">.</span><span class="na">getConstructor</span><span class="o">(</span><span class="n">String</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">      <span class="n">Log</span> <span class="n">log</span> <span class="o">=</span> <span class="n">candidate</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">LogFactory</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getName</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">      <span class="k">if</span> <span class="o">(</span><span class="n">log</span><span class="o">.</span><span class="na">isDebugEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="n">log</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Logging initialized using &#39;&#34;</span> <span class="o">+</span> <span class="n">implClass</span> <span class="o">+</span> <span class="s">&#34;&#39; adapter.&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">      <span class="o">}</span>
</span></span><span class="line"><span class="cl">      <span class="n">logConstructor</span> <span class="o">=</span> <span class="n">candidate</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">      <span class="k">throw</span> <span class="k">new</span> <span class="n">LogException</span><span class="o">(</span><span class="s">&#34;Error setting Log implementation.  Cause: &#34;</span> <span class="o">+</span> <span class="n">t</span><span class="o">,</span> <span class="n">t</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl">  <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>tryImplementation() 中调用了具体加载日志组件的方法，如果项目中未配置对象的组件，则会在 run() 中抛出异常
<code>java.lang.NoClassDefFoundError</code>，并在此方法中捕获，这里会忽略掉加载的异常。</p>
<p>注意判断条件 <code>logConstructor == null</code> 也就是说，只有加载失败时，才会向下执行继续加载下一个组件，如果加载成功了，则 logConstructor
是有值的。</p>
<p>setImplementation() 是具体加载日志组件的方法，如果加载成功，会对 logConstructor 进行赋值，并将具体使用的日志实现类进行日志打印。</p>
<h2 id="6-mybatis-log-规范-log">6 mybatis Log 规范 Log</h2>
<p>mybatis将不同组件的日志，统一封装成了四种日志级别。分别是 trace、debug、warn、error。</p>
<p>这四种日志级别，在 Log 接口中进行了定义。</p>
<p>源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">interface</span> <span class="nc">Log</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	
</span></span><span class="line"><span class="cl">  <span class="kt">boolean</span> <span class="nf">isDebugEnabled</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">  <span class="kt">boolean</span> <span class="nf">isTraceEnabled</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">  <span class="kt">void</span> <span class="nf">error</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">,</span> <span class="n">Throwable</span> <span class="n">e</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">  <span class="kt">void</span> <span class="nf">error</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">  <span class="kt">void</span> <span class="nf">debug</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">  <span class="kt">void</span> <span class="nf">trace</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">  <span class="kt">void</span> <span class="nf">warn</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">);</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="7-日志增强基-basejdbclogger">7 日志增强基 BaseJdbcLogger</h2>
<p>BaseJdbcLogger 是所有 jdbc 相关日志增强的基类，在这里定义了一些变量，用于缓存与数据库交互中传递的一些参数信息。</p>
<p>BaseJdbcLogger 数据结构如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">BaseJdbcLogger</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="cm">/** 保存preparestatment中常用的set方法（占位符赋值） */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">Set</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">SET_METHODS</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 保存preparestatment中常用的执行sql语句的方法 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">Set</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">EXECUTE_METHODS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashSet</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="cm">/** 保存preparestatment中set方法的键值对 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">Map</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">,</span> <span class="n">Object</span><span class="o">&gt;</span> <span class="n">columnMap</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashMap</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="cm">/** 保存preparestatment中set方法的key值 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">&gt;</span> <span class="n">columnNames</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 保存preparestatment中set方法的value值 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">&gt;</span> <span class="n">columnValues</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 日志对象 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kd">final</span> <span class="n">Log</span> <span class="n">statementLog</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kd">final</span> <span class="kt">int</span> <span class="n">queryStack</span><span class="o">;</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>在静态块中，对 SET_METHODS 以及 EXECUTE_METHODS 进行了初始化。</p>
<p>初始化源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">BaseJdbcLogger</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">static</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 反射获取 PreparedStatement 中所有 set 开头且有参数的方法名称
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">SET_METHODS</span> <span class="o">=</span> <span class="n">Arrays</span><span class="o">.</span><span class="na">stream</span><span class="o">(</span><span class="n">PreparedStatement</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getDeclaredMethods</span><span class="o">())</span>
</span></span><span class="line"><span class="cl">				<span class="o">.</span><span class="na">filter</span><span class="o">(</span><span class="n">method</span> <span class="o">-&gt;</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">().</span><span class="na">startsWith</span><span class="o">(</span><span class="s">&#34;set&#34;</span><span class="o">))</span>
</span></span><span class="line"><span class="cl">				<span class="o">.</span><span class="na">filter</span><span class="o">(</span><span class="n">method</span> <span class="o">-&gt;</span> <span class="n">method</span><span class="o">.</span><span class="na">getParameterCount</span><span class="o">()</span> <span class="o">&gt;</span> <span class="n">1</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">				<span class="o">.</span><span class="na">map</span><span class="o">(</span><span class="n">Method</span><span class="o">::</span><span class="n">getName</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">				<span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">Collectors</span><span class="o">.</span><span class="na">toSet</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="n">EXECUTE_METHODS</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;execute&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">EXECUTE_METHODS</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;executeUpdate&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">EXECUTE_METHODS</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;executeQuery&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">EXECUTE_METHODS</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;addBatch&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>并提供了一些设置参数以及获取参数值的字符串表示的方法：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span><span class="lnt">19
</span><span class="lnt">20
</span><span class="lnt">21
</span><span class="lnt">22
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">BaseJdbcLogger</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kt">void</span> <span class="nf">setColumn</span><span class="o">(</span><span class="n">Object</span> <span class="n">key</span><span class="o">,</span> <span class="n">Object</span> <span class="n">value</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">columnMap</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">key</span><span class="o">,</span> <span class="n">value</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">columnNames</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">key</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">columnValues</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">value</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">	
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="n">String</span> <span class="nf">getParameterValueString</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 将参数的值、参数类型，封装成string返回。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">List</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">&gt;</span> <span class="n">typeList</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;&gt;(</span><span class="n">columnValues</span><span class="o">.</span><span class="na">size</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="k">for</span> <span class="o">(</span><span class="n">Object</span> <span class="n">value</span> <span class="o">:</span> <span class="n">columnValues</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">value</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">typeList</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;null&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">typeList</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">objectValueString</span><span class="o">(</span><span class="n">value</span><span class="o">)</span> <span class="o">+</span> <span class="s">&#34;(&#34;</span> <span class="o">+</span> <span class="n">value</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getSimpleName</span><span class="o">()</span> <span class="o">+</span> <span class="s">&#34;)&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="kd">final</span> <span class="n">String</span> <span class="n">parameters</span> <span class="o">=</span> <span class="n">typeList</span><span class="o">.</span><span class="na">toString</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">parameters</span><span class="o">.</span><span class="na">substring</span><span class="o">(</span><span class="n">1</span><span class="o">,</span> <span class="n">parameters</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">-</span> <span class="n">1</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>还有一些其他方法，不再列举。</p>
<h2 id="8-连接日志增强-connectionlogger">8 连接日志增强 ConnectionLogger</h2>
<p>ConnectionLogger 实现了 InvocationHandler，且内部持有了 Connection 实例。它是 Connection 的日志增强类，从这个实现接口可以看出，使用的是 jdk 动态代理。</p>
<p>它的核心在 invoke 方法，源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span><span class="lnt">19
</span><span class="lnt">20
</span><span class="lnt">21
</span><span class="lnt">22
</span><span class="lnt">23
</span><span class="lnt">24
</span><span class="lnt">25
</span><span class="lnt">26
</span><span class="lnt">27
</span><span class="lnt">28
</span><span class="lnt">29
</span><span class="lnt">30
</span><span class="lnt">31
</span><span class="lnt">32
</span><span class="lnt">33
</span><span class="lnt">34
</span><span class="lnt">35
</span><span class="lnt">36
</span><span class="lnt">37
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">ConnectionLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 使用代理模式对连接进行日志增强。这里封装了连接对象 */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">Connection</span> <span class="n">connection</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Object</span> <span class="n">proxy</span><span class="o">,</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">params</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">			<span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果是 Object 中声明的方法，则直接跳过，执行业务方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">Object</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getDeclaringClass</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="k">this</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果是 prepareStatement 或者 prepareCall 方法，则参数列表中，第一个参数一定是 sql 语句，这里打印 sql 语句。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="s">&#34;prepareStatement&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">())</span> <span class="o">||</span> <span class="s">&#34;prepareCall&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">isDebugEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// 在打印sql语句的时候，将sql中的多余空白去除，替换为单个空格。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">debug</span><span class="o">(</span><span class="s">&#34; Preparing: &#34;</span> <span class="o">+</span> <span class="n">removeExtraWhitespace</span><span class="o">((</span><span class="n">String</span><span class="o">)</span> <span class="n">params</span><span class="o">[</span><span class="n">0</span><span class="o">]),</span> <span class="kc">true</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 调用业务方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">PreparedStatement</span> <span class="n">stmt</span> <span class="o">=</span> <span class="o">(</span><span class="n">PreparedStatement</span><span class="o">)</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">connection</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 创建 PreparedStatement 的代理对象，即对其进行日志增强，与此类相似。使用 PreparedStatementLogger 作为增强类。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">stmt</span> <span class="o">=</span> <span class="n">PreparedStatementLogger</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">stmt</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">stmt</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="s">&#34;createStatement&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果是 createStatement 方法，执行业务方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">Statement</span> <span class="n">stmt</span> <span class="o">=</span> <span class="o">(</span><span class="n">Statement</span><span class="o">)</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">connection</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 对 Statement 创建代理，使用 StatementLogger 作为增强类。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">stmt</span> <span class="o">=</span> <span class="n">StatementLogger</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">stmt</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">stmt</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span> <span class="k">else</span> <span class="o">{</span> <span class="c1">// 如果以上方法都不是，则直接执行业务方法。即只对上面两个 if 分支中判断的方法进行日志增强。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">connection</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">throw</span> <span class="n">ExceptionUtil</span><span class="o">.</span><span class="na">unwrapThrowable</span><span class="o">(</span><span class="n">t</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>在 invoke() 中，对 Connection 进行了日志增强，针对 prepareStatement()、prepareCall()、createStatement() 进行日志打印，并对其返回值生成代理。</p>
<p>还有一个生成 Connection 代理的方法：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt">1
</span><span class="lnt">2
</span><span class="lnt">3
</span><span class="lnt">4
</span><span class="lnt">5
</span><span class="lnt">6
</span><span class="lnt">7
</span><span class="lnt">8
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">ConnectionLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">static</span> <span class="n">Connection</span> <span class="nf">newInstance</span><span class="o">(</span><span class="n">Connection</span> <span class="n">conn</span><span class="o">,</span> <span class="n">Log</span> <span class="n">statementLog</span><span class="o">,</span> <span class="kt">int</span> <span class="n">queryStack</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">InvocationHandler</span> <span class="n">handler</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ConnectionLogger</span><span class="o">(</span><span class="n">conn</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">ClassLoader</span> <span class="n">cl</span> <span class="o">=</span> <span class="n">Connection</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getClassLoader</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="o">(</span><span class="n">Connection</span><span class="o">)</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">newProxyInstance</span><span class="o">(</span><span class="n">cl</span><span class="o">,</span> <span class="k">new</span> <span class="n">Class</span><span class="o">[]{</span><span class="n">Connection</span><span class="o">.</span><span class="na">class</span><span class="o">},</span> <span class="n">handler</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="9-preparedstatementlogger">9 PreparedStatementLogger</h2>
<p>与 ConnectionLogger 类似，它也是一个 InvocationHandler 实现类。内部持有了 PreparedStatement 对象。对一些特定方法添加了日志增强，
并对方法的返回值 ResultSet 生成代理对象。</p>
<p>源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span><span class="lnt">19
</span><span class="lnt">20
</span><span class="lnt">21
</span><span class="lnt">22
</span><span class="lnt">23
</span><span class="lnt">24
</span><span class="lnt">25
</span><span class="lnt">26
</span><span class="lnt">27
</span><span class="lnt">28
</span><span class="lnt">29
</span><span class="lnt">30
</span><span class="lnt">31
</span><span class="lnt">32
</span><span class="lnt">33
</span><span class="lnt">34
</span><span class="lnt">35
</span><span class="lnt">36
</span><span class="lnt">37
</span><span class="lnt">38
</span><span class="lnt">39
</span><span class="lnt">40
</span><span class="lnt">41
</span><span class="lnt">42
</span><span class="lnt">43
</span><span class="lnt">44
</span><span class="lnt">45
</span><span class="lnt">46
</span><span class="lnt">47
</span><span class="lnt">48
</span><span class="lnt">49
</span><span class="lnt">50
</span><span class="lnt">51
</span><span class="lnt">52
</span><span class="lnt">53
</span><span class="lnt">54
</span><span class="lnt">55
</span><span class="lnt">56
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">PreparedStatementLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">PreparedStatement</span> <span class="n">statement</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Object</span> <span class="n">proxy</span><span class="o">,</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">params</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 这个方法的增强内容，都是打印 debug 日志，在打印之前，判断 isDebugEnabled()，为了提高性能，
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="c1">// 因为打印的内容可能存在字符串拼装，相对判断一个布尔值，相对要消耗性能许多，而 debug 一般在生产环境并不会激活。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果是 Object 中声明的方法，则直接跳过，执行业务方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">Object</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getDeclaringClass</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="k">this</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// BaseJdbcLogger 中静态块中声明的方法集合。如果当前方法是集合中的方法，则打印日志。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">EXECUTE_METHODS</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果 debug 级别是开启的，则打印日志。打印内容是参数，比如一个 insert 语句，则这里会打印 mapper 方法中传递的参数及类型。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">isDebugEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">debug</span><span class="o">(</span><span class="s">&#34;Parameters: &#34;</span> <span class="o">+</span> <span class="n">getParameterValueString</span><span class="o">(),</span> <span class="kc">true</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 清除字段信息
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">clearColumnInfo</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果是 executeQuery 方法，则直接调用方法。并对 ResultSet 生成代理对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="s">&#34;executeQuery&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">ResultSet</span> <span class="n">rs</span> <span class="o">=</span> <span class="o">(</span><span class="n">ResultSet</span><span class="o">)</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span> <span class="n">rs</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">?</span> <span class="kc">null</span> <span class="o">:</span> <span class="n">ResultSetLogger</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">rs</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果是 setXXX 方法，且有方法参数，则将这些参数封装起来。 封装后执行具体的方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">SET_METHODS</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="s">&#34;setNull&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">setColumn</span><span class="o">(</span><span class="n">params</span><span class="o">[</span><span class="n">0</span><span class="o">],</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">setColumn</span><span class="o">(</span><span class="n">params</span><span class="o">[</span><span class="n">0</span><span class="o">],</span> <span class="n">params</span><span class="o">[</span><span class="n">1</span><span class="o">]);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果是 getResultSet 方法，则执行方法后，将 ResultSet 生成代理，进行日志增强。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="s">&#34;getResultSet&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">ResultSet</span> <span class="n">rs</span> <span class="o">=</span> <span class="o">(</span><span class="n">ResultSet</span><span class="o">)</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">rs</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">?</span> <span class="kc">null</span> <span class="o">:</span> <span class="n">ResultSetLogger</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">rs</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果是 getUpdateCount 方法，则在执行方法后，打印 debug 日志。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="s">&#34;getUpdateCount&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="kt">int</span> <span class="n">updateCount</span> <span class="o">=</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">updateCount</span> <span class="o">!=</span> <span class="o">-</span><span class="n">1</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">debug</span><span class="o">(</span><span class="s">&#34;   Updates: &#34;</span> <span class="o">+</span> <span class="n">updateCount</span><span class="o">,</span> <span class="kc">false</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">updateCount</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">statement</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">throw</span> <span class="n">ExceptionUtil</span><span class="o">.</span><span class="na">unwrapThrowable</span><span class="o">(</span><span class="n">t</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>创建 PreparedStatement 代理的方法：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt">1
</span><span class="lnt">2
</span><span class="lnt">3
</span><span class="lnt">4
</span><span class="lnt">5
</span><span class="lnt">6
</span><span class="lnt">7
</span><span class="lnt">8
</span><span class="lnt">9
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">PreparedStatementLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">static</span> <span class="n">PreparedStatement</span> <span class="nf">newInstance</span><span class="o">(</span><span class="n">PreparedStatement</span> <span class="n">stmt</span><span class="o">,</span> <span class="n">Log</span> <span class="n">statementLog</span><span class="o">,</span> <span class="kt">int</span> <span class="n">queryStack</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 使用当前类作为增强类，创建 PreparedStatement 的代理对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 符合单一职责原则，创建目标代理对象的工作应该交给与之相关的类来做，而本类就是目标类的增强。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">InvocationHandler</span> <span class="n">handler</span> <span class="o">=</span> <span class="k">new</span> <span class="n">PreparedStatementLogger</span><span class="o">(</span><span class="n">stmt</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">ClassLoader</span> <span class="n">cl</span> <span class="o">=</span> <span class="n">PreparedStatement</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getClassLoader</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="o">(</span><span class="n">PreparedStatement</span><span class="o">)</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">newProxyInstance</span><span class="o">(</span><span class="n">cl</span><span class="o">,</span> <span class="k">new</span> <span class="n">Class</span><span class="o">[]{</span><span class="n">PreparedStatement</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="n">CallableStatement</span><span class="o">.</span><span class="na">class</span><span class="o">},</span> <span class="n">handler</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="10-结果集日志增强-resultsetlogger">10 结果集日志增强 ResultSetLogger</h2>
<p>ResultSetLogger 实现了 InvocationHandler，是对 ResultSet 的日志增强。</p>
<p>invoke() 源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span><span class="lnt">11
</span><span class="lnt">12
</span><span class="lnt">13
</span><span class="lnt">14
</span><span class="lnt">15
</span><span class="lnt">16
</span><span class="lnt">17
</span><span class="lnt">18
</span><span class="lnt">19
</span><span class="lnt">20
</span><span class="lnt">21
</span><span class="lnt">22
</span><span class="lnt">23
</span><span class="lnt">24
</span><span class="lnt">25
</span><span class="lnt">26
</span><span class="lnt">27
</span><span class="lnt">28
</span><span class="lnt">29
</span><span class="lnt">30
</span><span class="lnt">31
</span><span class="lnt">32
</span><span class="lnt">33
</span><span class="lnt">34
</span><span class="lnt">35
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">ResultSetLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Object</span> <span class="n">proxy</span><span class="o">,</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">params</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果是 Object 中声明的方法，则直接跳过，执行业务方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">Object</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getDeclaringClass</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="k">this</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="n">Object</span> <span class="n">o</span> <span class="o">=</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">rs</span><span class="o">,</span> <span class="n">params</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 执行 next 方法，判断是否还有数据。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="s">&#34;next&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果当前方法是 next，返回值为 true，对变量自增，如果启用了 trace（比debug更低的级别） 级别，则打印 ResultSet 中的值。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">((</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">o</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">rows</span><span class="o">++;</span>
</span></span><span class="line"><span class="cl">					<span class="k">if</span> <span class="o">(</span><span class="n">isTraceEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="n">ResultSetMetaData</span> <span class="n">rsmd</span> <span class="o">=</span> <span class="n">rs</span><span class="o">.</span><span class="na">getMetaData</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">						<span class="kd">final</span> <span class="kt">int</span> <span class="n">columnCount</span> <span class="o">=</span> <span class="n">rsmd</span><span class="o">.</span><span class="na">getColumnCount</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">						<span class="k">if</span> <span class="o">(</span><span class="n">first</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">							<span class="n">first</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">							<span class="n">printColumnHeaders</span><span class="o">(</span><span class="n">rsmd</span><span class="o">,</span> <span class="n">columnCount</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">						<span class="o">}</span>
</span></span><span class="line"><span class="cl">						<span class="n">printColumnValues</span><span class="o">(</span><span class="n">columnCount</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">debug</span><span class="o">(</span><span class="s">&#34;     Total: &#34;</span> <span class="o">+</span> <span class="n">rows</span><span class="o">,</span> <span class="kc">false</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 清楚字段信息。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">clearColumnInfo</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="n">o</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">throw</span> <span class="n">ExceptionUtil</span><span class="o">.</span><span class="na">unwrapThrowable</span><span class="o">(</span><span class="n">t</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>创建 ResultSet 代理对象的方法源码：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
</span><span class="lnt"> 3
</span><span class="lnt"> 4
</span><span class="lnt"> 5
</span><span class="lnt"> 6
</span><span class="lnt"> 7
</span><span class="lnt"> 8
</span><span class="lnt"> 9
</span><span class="lnt">10
</span></code></pre></td>
<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">ResultSetLogger</span> <span class="kd">extends</span> <span class="n">BaseJdbcLogger</span> <span class="kd">implements</span> <span class="n">InvocationHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">static</span> <span class="n">ResultSet</span> <span class="nf">newInstance</span><span class="o">(</span><span class="n">ResultSet</span> <span class="n">rs</span><span class="o">,</span> <span class="n">Log</span> <span class="n">statementLog</span><span class="o">,</span> <span class="kt">int</span> <span class="n">queryStack</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 使用当前类作为增强类，创建 ResultSet 的代理对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 符合单一职责原则，创建目标代理对象的工作应该交给与之相关的类来做，而本类就是目标类的增强。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">InvocationHandler</span> <span class="n">handler</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ResultSetLogger</span><span class="o">(</span><span class="n">rs</span><span class="o">,</span> <span class="n">statementLog</span><span class="o">,</span> <span class="n">queryStack</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">ClassLoader</span> <span class="n">cl</span> <span class="o">=</span> <span class="n">ResultSet</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getClassLoader</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="o">(</span><span class="n">ResultSet</span><span class="o">)</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">newProxyInstance</span><span class="o">(</span><span class="n">cl</span><span class="o">,</span> <span class="k">new</span> <span class="n">Class</span><span class="o">[]{</span><span class="n">ResultSet</span><span class="o">.</span><span class="na">class</span><span class="o">},</span> <span class="n">handler</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="11-小结">11 小结</h2>
<p>对第三方日志组件的支出，通过适配器模式，对不同的日志组件，提供不同的适配器类，进行转换支持。</p>
<p>对不同节点的日志的打印支持，通过动态代理的方式，进行日志信息的增强。这样的好处是对原有业务方法是无侵入的，与业务功能解耦。</p>
<p>相较于 spring 中 aop 的实现原理是不同的，spring 中如果定义了许多增强方法，会将这些增强统一封装成一个 Advisor 列表。执行的时候，
会生成 MethodInterceptor 执行链。而代理对象，最终只生成一个，只是在代理对象的增强方法中，封装了这个执行链。</p>
<p>而 mybatis 中相对简单暴力一些，只是生成代理，就像使用 ConnectionLogger 增强创建 Connection 代理对象时，其内部封装的其实也是一个代理对象，
并非是原始链接。也就是说，在 mybatis 中对一个实例的多次增强，最终每一个增强都会创建代理对象。即对代理对象进行代理。</p></div>

        <div id="donateDiv"><a id="donate">打赏</a></div>
<div class="post-footer" id="post-footer">
    <div class="post-info">
        <div class="post-info-line">
            <div class="post-info-mod">
                <span>更新于 2020-12-20</span>
            </div>
            <div class="post-info-license"></div>
        </div>
        <div class="post-info-line">
            <div class="post-info-md"></div>
            <div class="post-info-share">
                <span></span>
            </div>
        </div>
    </div>

    <div class="post-info-more">
        <section class="post-tags"><i class="fas fa-tags fa-fw"></i>&nbsp;<a href="/tags/mybatis%E6%BA%90%E7%A0%81/">mybatis源码</a></section>
        <section>
            <span><a href="javascript:void(0);" onclick="window.history.back();">返回</a></span>&nbsp;|&nbsp;<span><a href="/">主页</a></span>
        </section>
    </div>

    <div class="post-nav"><a href="/posts/mybatis/01-mybatis-structure/" class="prev" rel="prev" title="01 Mybatis整体架构及开发设计原则"><i class="fas fa-angle-left fa-fw"></i>01 Mybatis整体架构及开发设计原则</a>
            <a href="/posts/mybatis/03-mybatis-pooled-data-source/" class="next" rel="next" title="03 Mybatis 连接池的实现原理">03 Mybatis 连接池的实现原理<i class="fas fa-angle-right fa-fw"></i></a></div>
</div>
<div id="comments"><div id="valine" class="comment"></div><noscript>
                Please enable JavaScript to view the comments powered by <a href="https://valine.js.org/">Valine</a>.
            </noscript></div></article></div>
            </main><footer class="footer">
        <div class="footer-container"><div class="footer-line">由 <a href="https://gohugo.io/" target="_blank" rel="noopener noreffer" title="Hugo 0.102.3">Hugo</a> 强力驱动 | 主题 - <a href="https://github.com/dillonzq/LoveIt" target="_blank" rel="noopener noreffer" title="LoveIt 0.2.10"><i class="far fa-kiss-wink-heart fa-fw"></i> LoveIt</a>
                </div><div class="footer-line"><i class="far fa-copyright fa-fw"></i><span itemprop="copyrightYear">2020 - 2024</span><span class="author" itemprop="copyrightHolder">&nbsp;<a href="https://wlizhi.cc" target="_blank">Wlizhi</a></span><span class="icp-splitter">&nbsp;|&nbsp;</span><br class="icp-br"/>
                    <span class="icp"><a href='https://beian.miit.gov.cn/' target='_blank'>豫ICP备17048163号<a/></span></div>
        </div>
    </footer></div>

        <div id="fixed-buttons"><a href="#" id="back-to-top" class="fixed-button" title="回到顶部">
                <i class="fas fa-arrow-up fa-fw"></i>
            </a><a href="#" id="view-comments" class="fixed-button" title="查看评论">
                <i class="fas fa-comment fa-fw"></i>
            </a>
        </div><link rel="stylesheet" href="/lib/valine/valine.min.css"><link rel="stylesheet" href="/lib/lightgallery/lightgallery.min.css"><script type="text/javascript" src="/lib/valine/Valine.min.js"></script><script type="text/javascript" src="/lib/smooth-scroll/smooth-scroll.min.js"></script><script type="text/javascript" src="/lib/autocomplete/autocomplete.min.js"></script><script type="text/javascript" src="/lib/algoliasearch/algoliasearch-lite.umd.min.js"></script><script type="text/javascript" src="/lib/lazysizes/lazysizes.min.js"></script><script type="text/javascript" src="/lib/lightgallery/lightgallery.min.js"></script><script type="text/javascript" src="/lib/lightgallery/lg-thumbnail.min.js"></script><script type="text/javascript" src="/lib/lightgallery/lg-zoom.min.js"></script><script type="text/javascript" src="/lib/clipboard/clipboard.min.js"></script><script type="text/javascript">window.config={"code":{"copyTitle":"复制到剪贴板","maxShownLines":35},"comment":{"valine":{"appId":"4yIHB0Rs1r3ykDVxayI5nqj3-gzGzoHsz","appKey":"ALr4H1hlK94girLDEUCGmp3o","avatar":"mp","el":"#valine","emojiCDN":"https://cdn.jsdelivr.net/npm/emoji-datasource-google@5.0.1/img/google/64/","emojiMaps":{"100":"1f4af.png","alien":"1f47d.png","anger":"1f4a2.png","angry":"1f620.png","anguished":"1f627.png","astonished":"1f632.png","black_heart":"1f5a4.png","blue_heart":"1f499.png","blush":"1f60a.png","bomb":"1f4a3.png","boom":"1f4a5.png","broken_heart":"1f494.png","brown_heart":"1f90e.png","clown_face":"1f921.png","cold_face":"1f976.png","cold_sweat":"1f630.png","confounded":"1f616.png","confused":"1f615.png","cry":"1f622.png","crying_cat_face":"1f63f.png","cupid":"1f498.png","dash":"1f4a8.png","disappointed":"1f61e.png","disappointed_relieved":"1f625.png","dizzy":"1f4ab.png","dizzy_face":"1f635.png","drooling_face":"1f924.png","exploding_head":"1f92f.png","expressionless":"1f611.png","face_vomiting":"1f92e.png","face_with_cowboy_hat":"1f920.png","face_with_hand_over_mouth":"1f92d.png","face_with_head_bandage":"1f915.png","face_with_monocle":"1f9d0.png","face_with_raised_eyebrow":"1f928.png","face_with_rolling_eyes":"1f644.png","face_with_symbols_on_mouth":"1f92c.png","face_with_thermometer":"1f912.png","fearful":"1f628.png","flushed":"1f633.png","frowning":"1f626.png","ghost":"1f47b.png","gift_heart":"1f49d.png","green_heart":"1f49a.png","grimacing":"1f62c.png","grin":"1f601.png","grinning":"1f600.png","hankey":"1f4a9.png","hear_no_evil":"1f649.png","heart":"2764-fe0f.png","heart_decoration":"1f49f.png","heart_eyes":"1f60d.png","heart_eyes_cat":"1f63b.png","heartbeat":"1f493.png","heartpulse":"1f497.png","heavy_heart_exclamation_mark_ornament":"2763-fe0f.png","hole":"1f573-fe0f.png","hot_face":"1f975.png","hugging_face":"1f917.png","hushed":"1f62f.png","imp":"1f47f.png","innocent":"1f607.png","japanese_goblin":"1f47a.png","japanese_ogre":"1f479.png","joy":"1f602.png","joy_cat":"1f639.png","kiss":"1f48b.png","kissing":"1f617.png","kissing_cat":"1f63d.png","kissing_closed_eyes":"1f61a.png","kissing_heart":"1f618.png","kissing_smiling_eyes":"1f619.png","laughing":"1f606.png","left_speech_bubble":"1f5e8-fe0f.png","love_letter":"1f48c.png","lying_face":"1f925.png","mask":"1f637.png","money_mouth_face":"1f911.png","nauseated_face":"1f922.png","nerd_face":"1f913.png","neutral_face":"1f610.png","no_mouth":"1f636.png","open_mouth":"1f62e.png","orange_heart":"1f9e1.png","partying_face":"1f973.png","pensive":"1f614.png","persevere":"1f623.png","pleading_face":"1f97a.png","pouting_cat":"1f63e.png","purple_heart":"1f49c.png","rage":"1f621.png","relaxed":"263a-fe0f.png","relieved":"1f60c.png","revolving_hearts":"1f49e.png","right_anger_bubble":"1f5ef-fe0f.png","robot_face":"1f916.png","rolling_on_the_floor_laughing":"1f923.png","scream":"1f631.png","scream_cat":"1f640.png","see_no_evil":"1f648.png","shushing_face":"1f92b.png","skull":"1f480.png","skull_and_crossbones":"2620-fe0f.png","sleeping":"1f634.png","sleepy":"1f62a.png","slightly_frowning_face":"1f641.png","slightly_smiling_face":"1f642.png","smile":"1f604.png","smile_cat":"1f638.png","smiley":"1f603.png","smiley_cat":"1f63a.png","smiling_face_with_3_hearts":"1f970.png","smiling_imp":"1f608.png","smirk":"1f60f.png","smirk_cat":"1f63c.png","sneezing_face":"1f927.png","sob":"1f62d.png","space_invader":"1f47e.png","sparkling_heart":"1f496.png","speak_no_evil":"1f64a.png","speech_balloon":"1f4ac.png","star-struck":"1f929.png","stuck_out_tongue":"1f61b.png","stuck_out_tongue_closed_eyes":"1f61d.png","stuck_out_tongue_winking_eye":"1f61c.png","sunglasses":"1f60e.png","sweat":"1f613.png","sweat_drops":"1f4a6.png","sweat_smile":"1f605.png","thinking_face":"1f914.png","thought_balloon":"1f4ad.png","tired_face":"1f62b.png","triumph":"1f624.png","two_hearts":"1f495.png","unamused":"1f612.png","upside_down_face":"1f643.png","weary":"1f629.png","white_frowning_face":"2639-fe0f.png","white_heart":"1f90d.png","wink":"1f609.png","woozy_face":"1f974.png","worried":"1f61f.png","yawning_face":"1f971.png","yellow_heart":"1f49b.png","yum":"1f60b.png","zany_face":"1f92a.png","zipper_mouth_face":"1f910.png","zzz":"1f4a4.png"},"enableQQ":true,"highlight":true,"lang":"zh-cn","meta":["nick","mail","link"],"pageSize":5,"placeholder":"昵称栏输入QQ，会使用QQ昵称和头像、并自动补充QQ邮箱到邮箱栏。\r\n正确填写邮箱更容易及时得到回复。\r\n说点什么吧...","recordIP":true,"visitor":true}},"lightGallery":{"actualSize":false,"exThumbImage":"data-thumbnail","hideBarsDelay":2000,"selector":".lightgallery","speed":400,"thumbContHeight":80,"thumbWidth":80,"thumbnail":true},"search":{"algoliaAppID":"1U459KF21F","algoliaIndex":"LoveItSite","algoliaSearchKey":"0433ffe95d71201a4f7c3e04b0125ac5","highlightTag":"em","maxResultLength":10,"noResultsFound":"没有找到结果","snippetLength":50,"type":"algolia"}};</script><script type="text/javascript" src="/js/theme.min.js"></script><script type="text/javascript" src="/js/donate.js"></script></body>
</html>
